mmc: at91_mci: wakeup on card insertion (or removal)

This piece of code enable the system to be wake-up by a card insertion or removal.

Signed-off-by: Marc Pignat <marc.pignat@hevs.ch>
Signed-off-by: Nicolas Ferre <nicolas.ferre@rfo.atmel.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>